Preterm birth reported to increase risk of psychiatric disorders

Preterm birth is an obstetric complication best avoided. In addition to increased infant mortality, infants born early suffer from a host of medical problems. A new study has reported that preterm birth significantly increases the risk of psychiatric disorders.

The study was published online on June 1 in the Archives of General Psychiatry by researchers affiliated with King’s College London, London, United Kingdom and Karolinska Institutet, Stockholm, Sweden.

The authors noted that preterm birth, intrauterine growth restriction, and delivery-related hypoxia (decreased oxygen) have been associated with schizophrenia. In view of this, they designed a study to assess the relationship between preterm birth and other psychiatric disorders that would surface in young adult life. The study group was comprised of 1,301,522 live-born individuals registered in the nationwide Swedish Medical Birth Register between 1973 and 1985 and living in Sweden at age 16 years by December 2002.

The following pregnancy outcomes were selected for analysis: gestational age at birth, birth weight for gestational age, and Apgar score at 5 minutes. Gestational age was estimated from the date of the mother’s last menstrual period; the following categories were assigned: very preterm (less than 32 gestational weeks), moderately preterm (32-36 gestational weeks), term (37-41 gestational weeks), and post-term (42 or more gestational weeks). The main outcome measures were psychiatric hospitalization with nonaffective psychosis, bipolar affective disorder, depressive disorder, eating disorder, drug dependency, or alcohol dependency, diagnosed according to the International Classification of Diseases codes for 8 through 10. Nonaffective psychosis refers to psychosis (major mental illness) not related to emotions or moods. Schizophrenia and delusional disorders are examples of nonaffective psychosis as opposed to bipolar disorder which is an affective psychosis because it involves emotional and mood abnormalities.

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The investigators found that preterm birth was significantly associated with increased risk of psychiatric hospitalization in adulthood (defined as 16 years of age or older) for a wide range of psychiatric disorders. Compared with term births (37-41 gestational weeks), infants born at 32 to 36 gestational weeks were 1.6 times more likely to have nonaffective psychosis, 1.3 times more likely to have depressive disorder, and 2.7 times more likely to have bipolar affective disorder. Those born at less than 32 weeks’ gestation were 2.5 times more likely to have nonaffective psychosis, 2.9 times more likely to have depressive disorder, and 7.4 times more likely to have bipolar affective disorder.

The authors concluded that the risk of hospitalization for a psychiatric disorders may increase with younger gestational age. Furthermore, similar associations were not observed for non-optimal fetal growth and low Apgar score.

The authors noted that a limitation of the study included the fact that psychiatric diagnoses were studied in relation to hospitalization; therefore, only the more severe psychiatric cases were included in the analyses. Another limitation was that gestational age was determined by last menstrual period rather than an early ultrasound. Gestational age assumes that conception occurs two weeks after the last menstrual period. That date is subject to error from patient recall as well as an episode of bleeding that was assumed to be the last menstrual period. An early ultrasound is accurate within a week. Despite these limitations, the study clearly indicated an increased risk of psychiatric illness in adult life for preterm infants.